/P\ r.i.n.c.e.s.s [@}} m e r c u r y ++ past life
The manga tells a short history of the senshi as daughters of their respective planets towards the end of the Dream manga arc. Sailormoon uses the power of the silver crystal to reveal the true identity of the soldiers. This foreshadows the close of the BSSM chapter by slowly connecting things to the Silver Millenium and the beginnings of the story.
/P\ r.i.n.c.e.s.s [@}} m e r c u r y ++ princess of a planet
During the time of the Silver Millenium, each planet had a princess who lived in the designated castle of their mother planets. Act 41 reveals the name, the purpose, and the power each castle holds. Nehelenia has stolen the Mystical Silver Crystal and holds the senshi in her hands. But Usagi, with the power of love, gathers her strength to become Princess Serenity, harboring the glow of the golden crescent moon on her forehead.
And power cannot be created alone ... nor can it be used alone.
I'll show you what our power is made of!!"
She streches her hands to the sky and a light shines above her. The light spreads and covers the Sailor Senshi, transforming their sailor fuku into their Princess dresses. Suddenly, miniature versions of the soldiers appear in front of them, calling themselves "sailor super guardians." They endear the senshi to borrow the power from their mother planets and give Sailormoon their powers. A new holy chalice appears above Usagi's head and she pleads for everyone's power. Each senshi calls out the name of their planets and Usagi transforms into EternalSailormoon, "carrier of the closest power to that of the Queen."
/P\ r.i.n.c.e.s.s [@}} m e r c u r y ++ mariner castle
Merc's castle is revealed to be the "Mariner Castle," the first to give its power to the new holy chalice. Each castle is named after a moon orbitting the planet (Venus's castle is called "Io," Neptune's castle is called "Triton," etc.). Only the pictures of Uranus, Neptune, and Pluto's castle are shown in Act 45, so a physical description of the Mariner is not available. The planet Mercury has no known moon; so, than name "Mariner Castle" may be based on the first man-made satellite to orbit Mercury, the Mariner. The Mariner 10, to be exact, launched in 1973 and utilized the gravity of Venus in order to take the earliest close-up pictures of both Venus's and Mercury's surfaces. Another theory is the root word of Mariner, "marine." "Marine" relates to anything of the sea including soldiers, maritime travel/laws, and paintings of the sea. The color of marine is also generally a dark blue, Mercury's most recognized color.
1 Princess Serenity. Act 41. Sailormoon Manga.
2 Mariner 10. NinePlanets.org.
3 "Marine." Wikipedia.org.